Synthesis and characterization of polyaryl blend membranes having different composition, different covalent and/or ionical cross-linking density, and their application to DMFC

In this contribution, different ionomer blend membrane types which show high proton conductivity, thermal stability, and good direct methanol fuel cell (DMFC) performance, are presented: (1) Covalently cross-linked blend membranes from polyaryl sulfinates and polyaryl sulfonates where the sulfinate groups were crosslinked by alkylation with 1,4diiodobutane; (2) ionically cross-linked blend membranes from polyaryl sulfonates and poly(het)aryl N bases; (3) covalent-ionically cross-linked blend membranes from polyaryl sulfinates, polyaryl sulfonates, and poly(het)aryl N bases; and (4) blend membranes which additionally contain an inorganic compound. The inorganic compound was mixed into the membrane. As aryl polymers, different poly(ethersulfone)s and different poly(etherketone)s have been used, as hetaryl N base, polybenzimidazole PBI Celazole(R) has been applied. The membrane characterization yielded the following results: (1) high proton conductivities of the membranes could be realized; (2) the TEM micrographs showed that phase-separated or homogeneous morphologies could be realized in the membranes; (3) the DMFC application of the membranes showed that the developed nonfluorinated ionomer membranes have a DMFC performance comparable to perfluorinated ionomer membranes, reaching peak power densities of around 0.25 W/cm(2) at 110degreesC. It was also found that the addition of SiO2 powder dramatically reduced the MeOH permeability, but also led to a worse DMFC performance, probably caused by a worse contact membrane-electrode because of a rougher membrane surface caused by the inorganic compound.